Overcoming the Fear of IPv6

A few years back I set up IPv6 connectivity on my home network for the first time. I had a rush of exhilaration when the first ping and traceroute commands completed successfully. Suddenly, I was free of Network Address Translation and bypassing my firewall, connecting directly to any IPv6 device on the Internet. But then it slowly dawned on me that those people same people could also directly connect to my device! In a panic, I wondered if my SMB shares were visible to the world, or if criminals could relentlessly probe my open ports for zero-day vulnerabilities. How could I even check if I had any open ports? My fear got the best of me and I disabled IPv6.

I contacted my friend Dan and posed my dilemma to him. How could I tell if my ports were locked down on a machine which ran IPv6? A number of sites provided port scanners for IPv4, but nobody had a general purpose scanner for IPv6. Hurricane Electric provided one, but only for devices that were on their network. Dan hacked up a primitive IPv6 open port testing site, which uses NMAP to scan an IPv6 visitor for typically vulnerable ports before issuing a simple report. I was pleased to discover that my computer did not answer on any of those commonly attacked ports.

In this process, I discovered that many modern operating systems with IPv6 enabled also come with a set of reasonable host firewall defaults which do not expose listening ports as much as I had expected based on my experience with IPv4. Many hosts with IPv6 enabled by default also come with some very sensible settings to prevent network-launched crimes of opportunity from malicious users.

IPv6 also provides a natural defense against classic portscanning attacks, where an attacker probes for commonly vulnerable ports of every IP address on a subnet. For densely packed IPv4 service provider networks with one IP address assigned per typical user, a few thousand probes across a known DSL or cable subnet can yield a rich collection of potential targets. Since the address space of IPv6 is so much larger and sparsely populated than IPv4, blind portscanning of subnets becomes impractical since a typical IPv6 subnet contains quintillions of addresses hosting a relatively small number of end devices.

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